Spin valves with enhanced GMR and thermal stability

ABSTRACT

An SV sensor with the preferred structure Substrate/Seed/Free/Spacer/Pinned/AFM/Cap where the seed layer is a non-magnetic Ni--Fe--Cr or Ni--Cr film and the AFM layer is preferably Ni--Mn. The non-magnetic Ni--Fe--Cr seed layer results in improved grain structure in the deposited layers enhancing the GMR coefficients and the thermal stability of the SV sensors. The improved thermal stability enables use of Ni--Mn with its high blocking temperature and strong pinning field as the AFM layer material without SV sensor performance degradation from the high temperature anneal step needed to develop the desired exchange coupling.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to spin valve magnetic transducers forreading information signals from a magnetic medium and, in particular,to a spin valve sensor with enhanced GMR effect and improved thermalstability.

2. Description of Related Art

Computers often include auxiliary memory storage devices having media onwhich data can be written and from which data can be read for later use.A direct access storage device (disk drive) incorporating rotatingmagnetic disks is commonly used for storing data in magnetic form on thedisk surfaces. Data is recorded on concentric, radially spaced tracks onthe disk surfaces. Magnetic heads including read sensors are then usedto read data from the tracks on the disk surfaces.

In high capacity disk drives, magnetoresistive read sensors, commonlyreferred to as MR heads, are the prevailing read sensors because oftheir capability to read data from a surface of a disk at greater lineardensities than thin film inductive heads. An MR sensor detects amagnetic field through the change in the resistance of its MR sensinglayer (also referred to as an "MR element") as a function of thestrength and direction of the magnetic flux being sensed by the MRlayer.

The conventional MR sensor operates on the basis of the anisotropicmagnetoresistive (AMR) effect in which an MR element resistance variesas the square of the cosine of the angle between the magnetization inthe MR element and the direction of sense current flow through the MRelement. Recorded data can be read from a magnetic medium because theexternal magnetic field from the recorded magnetic medium (the signalfield) causes a change in the direction of magnetization in the MRelement, which in turn causes a change in resistance in the MR elementand a corresponding change in the sensed current or voltage.

Another type of MR sensor is the giant magnetoresistance (GMR) sensormanifesting the GMR effect. In GMR sensors, the resistance of the MRsensing layer varies as a function of the spin-dependent transmission ofthe conduction electrons between magnetic layers separated by anon-magnetic layer (spacer) and the accompanying spin-dependentscattering which takes place at the interface of the magnetic andnon-magnetic layers and within the magnetic layers.

GMR sensors using only two layers of ferromagnetic material (e.g.,Ni--Fe) separated by a layer of non-magnetic material (e.g., copper) aregenerally referred to as spin valve (SV) sensors manifesting the SVeffect. In an SV sensor, one of the ferromagnetic layers, referred to asthe pinned layer, has its magnetization typically pinned by exchangecoupling with an antiferromagnetic (e.g., NiO or Fe--Mn) layer. Thepinning field generated by the antiferromagnetic layer should be greaterthan demagnetizing fields (about 200 Oe) at the operating temperature ofthe SV sensor (about 120 C.) to ensure that the magnetization directionof the pinned layer remains fixed during the application of externalfields (e.g., fields from bits recorded on the disk). The magnetizationof the other ferromagnetic layer, referred to as the free layer,however, is not fixed and is free to rotate in response to the fieldfrom the recorded magnetic medium (the signal field). In the SV sensor,the SV effect varies as the cosine of the angle between themagnetization of the pinned layer and the magnetization of the freelayer. Recorded data can be read from a magnetic medium because theexternal magnetic field from the recorded magnetic medium (the signalfield) causes a change in direction of magnetization in the free layer,which in turn causes a change in resistance of the SV sensor and acorresponding change in the sensed current or voltage. IBM's U.S. Pat.No. 5,206,590 granted to Dieny et al., incorporated herein by reference,discloses an GMR sensor operating on the basis of the SV effect.

FIG. 1 shows a prior art SV sensor 100 comprising end regions 104 and106 separated by a central region 102. A free layer (free ferromagneticlayer) 110 is separated from a pinned layer (pinned ferromagnetic layer)120 by a non-magnetic, electrically-conducting spacer 115. Themagnetization of the pinned layer 120 is fixed by an antiferromagnetic(AFM) layer 125. Free layer 110, spacer 115, pinned layer 120 and theAFM layer 125 are all formed in the central region 102. Hard bias layers130 and 135 formed in the end regions 104 and 106, respectively, providelongitudinal bias for the free layer 110. Leads 140 and 145 formed overhard bias layers 130 and 135, respectively, provide electricalconnections for the flow of the sensing current I_(S) from a currentsource 160 to the MR sensor 100. Sensing means 170 connected to leads140 and 145 sense the change in the resistance due to changes induced inthe free layer 110 by the external magnetic field (e.g., field generatedby a data bit stored on a disk).

As mentioned above, the magnetization of the pinned layer 120 in theprior art SV sensor 100 is generally fixed through exchange couplingwith AFM layer 125 of antiferromagnetic material such as Fe--Mn or NiO.However, both Fe--Mn and NiO have rather low blocking temperatures(blocking temperature is the temperature at which the pinning field fora given material reaches zero Oe) which make their use as an AFM layerin an SV sensor difficult and undesirable.

A desirable alternate AFM material is Ni--Mn which has better corrosionproperties than Fe--Mn, very large exchange pinning at room temperature,and much higher blocking temperature than either Fe--Mn or NiO. Highblocking temperature is essential for SV sensor reliability since SVsensor operating temperatures can exceed 120 C. in some applications.

Referring to FIG. 2, there is shown the change in the unidirectionalanisotropy field (H_(UA)) or pinning field versus temperature for 50 Athick Ni--Fe pinned layers using Fe--Mn, NiO and Ni--Mn as the pinninglayers. Fe--Mn has a blocking temperature of about 180 C. (curve 210)and NiO has a blocking temperature of about 220 C. (curve 220).Considering that a typical SV sensor used in a magnetic recording diskdrive should be able to operate reliably at a constant temperature ofabout 120 C. with a pinning field of at least 200 Oe, it can readily beseen that Fe--Mn substantially loses it ability to pin the pinned layerat about 120 C. (pinning field dropping to about 150 Oe) and NiO canonly marginally provide adequate pinning at about 120 C. (pinning fielddropping to about 170 Oe). It should be noted that once the pinningeffect is lost, the SV sensor loses its SV effect either totally orpartially, rendering the SV sensor useless. In contrast, it can be seenin FIG. 2 that Ni--Mn with a blocking temperature of beyond 450 C.(curve 230) easily meets the pinning field requirements at the 120 C.operating temperature of typical SV sensors.

However, the problem with using Ni--Mn AFM for the pinning layer is therequirement for a high temperature (equal or greater than 240 C.)annealing step after the deposition of the SV sensor layers(post-annealing) to achieve the desired exchange coupling between theNi--Mn pinning layer and the Ni--Fe pinned layer in order to achieveproper SV sensor operation. Unfortunately, annealing at such hightemperature (equal or greater than 240 C.) substantially degrades theGMR coefficient of the SV sensor. This irreversible degradation of theSV sensor is believed to be caused by interdiffusion at the interfacesbetween the Cu spacer layer and the adjacent magnetic layers. Stabilityagainst Cu interdiffusion is a prerequisite for the use of Ni--Mn as theAFM layer in a SV sensor because the SV sensor must survive the severeheat treatment required to anneal the Ni--Mn.

Therefore there is a need for a SV sensor using a Ni--Mn AFM pinninglayer that can withstand the annealing step required to achieve thedesired exchange coupling without the undesirable degradation of the SVeffect.

SUMMARY OF THE INVENTION

It is an object of the present invention to disclose an improved seedlayer for SV sensors with the film structureSeed/Free/Spacer/Pinned/AFM/Cap wherein the improved seed layer resultsin enhanced GMR effect and improved thermal stability.

It is another object of the present invention to disclose an SV sensorhaving an improved seed layer which allows the use of a Ni--Mn AFM layeras the pinning layer.

It is a further object of the present invention to disclose an improvedSV sensor having the film structure Ni--Fe--Cr/Ni--Fe/Cu/Co/Ni--Mn/Capwherein the annealing step to develop exchange coupling is carried outwithout degradation of the GMR effect.

It is yet another object of the present invention to disclose a processfor optimizing the Ni--Fe--Cr seed layer thickness for fabrication of SVsensors with the film structure Ni--Fe--Cr/Ni--Fe/Cu/Co/Ni--Mn/Cap.

In accordance with the principles of the present invention there isdisclosed an SV sensor with the preferred structure ofSubstrate/Ni--Fe--Cr/Ni--Fe/Cu/Co/Ni--Mn/Cap. The Ni--Fe--Cr seed layeralters the grain structure of the subsequent layers deposited over saidseed layer resulting in improved GMR effect and improved thermalstability of the SV sensor. The layers deposited over the Ni--Fe--Crseed layer have significantly larger grain structures than are obtainedwith a tantalum (Ta) seed layer. The larger grain structures of the SVsensor layers are thought to be less susceptible to interdiffusion atinterfaces between adjoining layers.

The above as well as additional objects, features, and advantages of thepresent invention will become apparent in the following detailed writtendescription.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings. In the following drawings, like referencenumerals designate like or similar parts throughout the drawings.

FIG. 1 is an air bearing surface view of a prior art SV sensor;

FIG. 2 is a graph showing temperature dependence of the pinning fieldsfor exchange coupling of Fe--Mn, NiO and Ni--Mn antiferromagneticpinning layers to Ni--Fe ferromagnetic pinned layers;

FIG. 3 is a simplified drawing of a magnetic recording disk drive systemincorporating the SV sensor of the present invention;

FIG. 4 is an air bearing surface view of the SV sensor of the presentinvention;

FIG. 5 is a graph showing the GMR coefficient (deltaR/R) as a functionof Ni--Fe--Cr seed layer thickness for an SV sensor with Ni--Mn AFMlayer; and

FIG. 6 is an air bearing surface view of an alternative embodiment of anSV sensor of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description is the best embodiment presently contemplatedfor carrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.

Referring now to FIG. 3, there is shown a disk drive 300 embodying thepresent invention. As shown in FIG. 3, at least one rotatable magneticdisk 312 is supported on a spindle 314 and rotated by a disk drive motor318. The magnetic recording media on each disk is in the form of anannular pattern of concentric data tracks (not shown) on disk 312.

At least one slider 313 is positioned on the disk 312, each slider 313supporting one or more magnetic read/write heads 321 where the head 321incorporates the MR sensor of the present invention. As the disksrotate, slider 313 is moved radially in and out over disk surface 322 sothat heads 321 may access different portions of the disk where desireddata is recorded. Each slider 313 is attached to an actuator arm 319 bymeans of a suspension 315. The suspension 315 provides a slight springforce which biases slider 313 against the disk surface 322. Eachactuator arm 319 is attached to an actuator means 327. The actuatormeans as shown in FIG. 3 may be a voice coil motor (VCM). The VCMcomprises a coil movable within a fixed magnetic field, the directionand speed of the coil movements being controlled by the motor currentsignals supplied by controller 329.

During operation of the disk storage system, the rotation of disk 312generates an air bearing between slider 313 (the surface of slider 313which includes head 321 and faces the surface of disk 312 is referred toas an air bearing surface (ABS)) and disk surface 322 which exerts anupward force or lift on the slider. The air bearing thuscounter-balances the slight spring force of suspension 315 and supportsslider 313 off and slightly above the disk surface by a small,substantially constant spacing during normal operation.

The various components of the disk storage system are controlled inoperation by control signals generated by control unit 329, such asaccess control signals and internal clock signals. Typically, controlunit 329 comprises logic control circuits, storage means and amicroprocessor. The control unit 329 generates control signals tocontrol various system operations such as drive motor control signals online 323 and head position and seek control signals on line 328. Thecontrol signals on line 328 provide the desired current profiles tooptimally move and position slider 313 to the desired data track on disk312. Read and write signals are communicated to and from read/writeheads 321 by means of recording channel 325.

The above description of a typical magnetic disk storage system, and theaccompanying illustration of FIG. 3 are for representation purposesonly. It should be apparent that disk storage systems may contain alarge number of disks and actuators, and each actuator may support anumber of sliders.

FIG. 4 shows an air bearing surface (ABS) view of the SV sensor 400according to the preferred embodiment of the present invention. SVsensor 400 comprises end regions 404 and 406 separated by a centralregion 402. The substrate 450 can be any suitable substance, includingglass, semiconductor material, or a ceramic material, such as alumina(Al₂ O₃). The seed layer 440 is a layer deposited to modify thecrystallographic texture or grain size of the subsequent layers. Inprevious SV structures, the seed layer material commonly used istantalum (Ta). In the present invention, an improved seed layer 440 isformed of Ni--Fe (or Ni), mixed with enough chromium (Cr) to make theresulting alloy non-magnetic. A free layer (free ferromagnetic layer)410, deposited on the seed layer 440, is separated from a pinned layer(pinned ferromagnetic layer) 420 by a non-magnetic spacer layer 415. Inthe preferred embodiment of the present invention, spacer layer 415 isalso an electrically conducting spacer layer. Free layer 410 may be madeof a single layer of ferromagnetic material or it may be made of a firstand second free sub-layers of different ferromagnetic materials wherethe second sub-layer is formed over the seed layer 440 and the firstsub-layer is formed in contact with the spacer layer 415. Themagnetization of the pinned layer 420 is fixed by an antiferromagnetic(AFM) layer 430. A cap layer 405 deposited on the AFM layer 430completes the central region 402 of the SV sensor 400.

Referring to FIG. 4, the SV sensor 400 further comprises layers 434 and436 formed on the end regions 404 and 406, respectively, for providing alongitudinal bias field to the free layer 410 to ensure a singlemagnetic domain state in the free layer. Lead layers 460 and 465 arealso deposited on the end regions 404 and 406, respectively, to provideelectrical connections for the flow of the sensing current I_(S) from acurrent source 470 to the SV sensor 400. Sensing means 480 connected toleads 460 and 465 sense the change in the resistance due to changesinduced in the free layer 410 by the external magnetic field (e.g.,field generated by a data bit stored on a disk). Sensing means 480includes a digital or analog recording channel. In the preferredembodiment of the present invention, sensing means 480 includes arecording channel known as partial-response maximum-likelihood (PRML)recording channel. Design and implementation of the PRML recordingchannels are well known to those skilled in the art.

The SV sensor of the present invention is fabricated using sputteringmethods known in the art (ion beam, R-F diode, magnetron or DC magnetronsputtering) to sequentially deposit the layers of SV sensor 400 shown inFIG. 4. The sputter deposition process for fabrication of SV sensor 400is started with deposition on a substrate 450 of a seed layer 440 havinga thickness of about 40 Å. Seed layer 440 is formed of an alloyNi--Fe--Cr, or alternatively Ni--Cr, having sufficient chromium (Cr)content to make the alloy non-magnetic. In the preferred embodiment ofthis invention, the composition of the seed layer in atomic percent is60% (Ni₈₀ --Fe₂₀) and 40% Cr. Alternatively, the Ni--Fe--Cr alloycomposition in atomic percent may be expressed as:

    (Ni.sub.a --Fe.sub.b).sub.x --Cr.sub.y

where

a+b=100%, 45%<a<100%, 0%<b<55%, and

x+y=100%, 50%<x<80%, 20%<y<50%.

Free layer 410 formed of a permalloy (Ni--Fe) film having a thickness ofabout 55 Å is deposited on and in contact with seed layer 440.Alternatively, free layer 410 may be formed as a laminated structurecomprising a Ni--Fe layer having a thickness of about 45 Å deposited onand in contact with seed layer 440 and a cobalt (Co) layer having athickness of about 6 Å deposited on and in contact with the Ni--Felayer. Spacer layer 415 formed of a copper (Cu) film having a thicknessof about 24 Å is deposited on and in contact with the free layer 410.Pinned layer 420 formed of a cobalt (Co) film having a thickness ofabout 30 Å is deposited on and in contact with the spacer layer 415. AFMlayer 430 formed of a Ni--Mn film having a thickness of about 300 Å isdeposited on and in contact with the pinned layer 420. The preferredcomposition of the Ni--Mn AFM layer is a Mn composition in the rangebetween 46 and 60 atomic percent. Cap layer 405 formed of a suitableprotective material such as Ta, Ni--Fe--Cr or Al₂ O₃ completes thestructure of the central portion 402 of the SV sensor 400.

The as-deposited Ni--Mn AFM layer 430 does not show significant exchangecoupling to pinned layer 420. To develop the desired exchange coupling,SV sensor 400 is thermally annealed at a temperature of 280 C. for 4hours. Annealing conditions used to develop exchange coupling can bevaried from about 240 C. for greater than 8 hours to 320 C. for greaterthan 0.2 hours. In the present invention, the use of Ni--Fe--Cr as theseed layer for SV sensor 400 results in a Ni--Fe free layer grainstructure with grains four to five times larger than obtained for freelayer deposition on a Ta seed layer. The increased grain size of thefree layer 410 also results in a larger grain structure of thesubsequently deposited layers comprising SV sensor 400. Since in thinfilms most of the diffusion at temperatures below 300 C. occurs at grainboundaries, therefore it is postulated that the reduced number of grainboundaries resulting from the larger grain structure inhibitsinterdiffusion. After the annealing process at 280 C. for 4 hours to setthe Ni--Mn AFM layer exchange coupling with the pinned layer, the SVsensors have GMR coefficients, deltaR/R, as high as 7.7%, an improvementof 70% over comparable SV sensors fabricated by the same process butwith a Ta seed layer.

In the preferred embodiment of the invention, SV sensors may be formedwith the alternate free layer 410 comprising laminated Ni--Fe and Colayers. In this structure, the laminated free layer 410 comprises aNi--Fe layer (second sub-layer) having a thickness of about 45 Å and aCo layer (first sub-layer) having a thickness of about 6 Å. The magneticthickness of this laminated free layer structure is equivalent to themagnetic thickness of the 55 Å thick Ni--Fe free layer used in theembodiment described above. After annealing at 280 C. for 4 hours, GMRcoefficients of 10.5% were obtained for SV sensors having the laminatedNi--Fe/Co free layer structure.

FIG. 5 is a graph showing the effect of seed layer thickness on the GMRcoefficient for SV sensors with Ni--Fe--Cr seed layers and Ni--Mn AFMlayers. The data is shown for SV sensors after annealing at 280 C. for 4hours. The GMR coefficient increases with thickness of the Ni--Fe--Crseed layer, reaching a maximum value of 7.7% at about 40 to 50 Å. TheGMR coefficient of a comparable SV sensor fabricated with a 50 Å thickTa seed layer is 4.5%.

The Ni--Fe--Cr seed layer of the present invention makes it possible touse Ni--Mn as the AFM layer for pinning without suffering degradation ofthe SV sensor GMR coefficient. The improved pinning provided by Ni--Mnis evident from measurements of the pinning reversal field (sum ofpinning field and the coercive field, H_(c)). For the Ni--Mn AFM SVsensors of this invention the pinning reversal field is about 1100 Oe(for Ni--Fe--Cr seed layer thickness between 20 Å and 50 Å). This highexchange pinning field together with the high blocking temperature(about 450 C.) of Ni--Mn AFM layers prevents any pinned layer rotationfrom degrading SV sensor efficiency even at operating temperaturesexceeding 120 C. For comparison, the pinning reversal field of Fe--MnAFM SV sensors is only about 300 Oe and the blocking temperature isabout 180 C. With the Fe--Mn AFM SV sensors, significant pinned layerrotation can occur due to diminished exchange pinning at temperaturesabove 120 C.

The improved temperature stability of the Ni--Mn AFM SV sensors of thepresent invention has the added advantage over previous SV sensors thathigher values of the sense current I_(S) can be applied across thesensor resulting in larger signals measured by the sensing means as SVsensor resistance changes in response to applied magnetic fields. Theability to operate SV sensors at higher sensitivities afforded by highersense current without signal degradation due to the accompanyingtemperature increase can be a significant advantage as SV sensors becomesmaller in high data density applications.

While the preferred embodiment of the present invention provides thegreatest improvement in SV sensor thermal stability, it will be apparentto those skilled in the art that the use of a Ni--Fe--Cr seed layer canimprove the GMR coefficient and the thermal stability of SV sensorsusing other AFM layer materials. The present inventors have fabricatedSV sensors with Fe--Mn AFM layers using the Ni--Fe--Cr seed layer andhaving the general structure Seed/Free/Spacer/Pinned/AFM/Cap. With theFe--Mn AFM layer, exchange coupling to the pinned layer is present inthe as-deposited state without requiring an annealing process. With anoptimized seed layer thickness of about 50 Å, the GMR coefficient isabout 8.5% which is an improvement by 40% over the GMR coefficientobtained for the same structure fabricated with a Ta seed layer 50 Åthick. The thermal stability of the GMR coefficient for an SV sensorhaving the Ni--Fe--Cr seed layer of the present invention is alsoimproved compared to the Ta seed layer SV sensors. After a 280 C. annealfor 4 hours, the Ni--Fe--Cr seed layer (50 Å thick) SV sensor GMRcoefficient degraded by only 2% compared to 45% degradation for the Taseed layer (50 Å thick) SV sensors. However, unlike the results for theNi--Mn AFM SV sensors, with the Fe--Mn AFM SV sensors the pinned layerreversal field decreases as the seed layer thickness is increased anddegrades further with annealing at 280 C. for 4 hours.

Experiments by the present inventors have shown that optimal thicknessof the Ni--Fe--Cr seed layer for the preferred embodiment is differentfor different sputter deposition systems. It is believed that theimproved grain structure of the deposited layers comprising the SVsensors can vary to some degree depending on exact conditions in eachdeposition system. Because of this variability, an optimizationprocedure must be followed to determine the Ni--Fe--Cr seed layerthickness that results in the best SV sensor performance for theparticular ion beam deposition system being used. The preferredprocedure is to carry out a series of SV sensor depositions using arange of seed layer thicknesses and keeping all other parametersconstant. A suitable thickness range for the seed layer thicknesses is10 Å to 100 Å. After a 280 C. anneal for 4 hours, the GMR coefficientsand exchange coupling parameters are measured by methods well known inthe art and optimal seed layer thickness is determined.

FIG. 6 shows an air bearing surface (ABS) view of SV sensor 600according to an alternative embodiment of the present invention similarto the SV sensor 400 wherein the pinned layer 420 of the SV sensor 400is replaced by a laminated antiparallel-pinned (AP-pinned) layer 620.The PF₁ /APC/PF₂ laminated AP-pinned layer 620 is formed on spacer layer415. The laminated AP-pinned layer 620 comprises a first ferromagneticpinned layer 622 (PF₁) and a second ferromagnetic pinned layer 626 (PF₂)separated from each other by an antiparallel coupling (APC) layer 624 ofnon-magnetic material that allows PF₁ and PF₂ to be strongly coupledtogether antiferromagnetically. The two pinned layers PF₁, PF₂ in thelaminated AP-pinned layer structure 620 have their magnetizationsdirections oriented antiparallel, as indicated by arrows 627 and 628(arrow heads pointing in and out of the plane of the paper). Theantiparallel alignment of the magnetizations of the two ferromagneticlayers PF₁, PF₂ is due to an antiferromagnetic exchange coupling throughthe APC layer 624. The APC layer 624 is preferably made of ruthenium(Ru) although it may also be made of iridium (Ir) or rhodium (Rh). AFMlayer 430 is deposited on and in contact with the second ferromagneticlayer 626 (PF₂). In the formation of SV sensor 600, the use of theNi--Fe--Cr material of the present invention for seed layer 440 willimprove the grain structure of the deposited films resulting in improvedGMR coefficient and thermal stability.

It will be apparent to those skilled in the art that alternative AFMlayer 430 materials such as Fe--Mn, Pd--Mn, Pt--Mn, Pd--Pt--Mn, Ir--Mn,Rh--Mn, Cr--Mn--Pt and Ru--Mn may also be used to fabricate SV sensorsaccording to the present invention.

It will also be apparent to those skilled in the art that alternativenon-magnetic spacer layer 415 materials such as gold and silver may alsobe used to fabricate SV sensors according to the present invention.

It will be further apparent to those skilled in the art that alternativepinned layer 420 materials such as permalloy (Ni--Fe) and laminatedmultilayer films such as Ni--Fe/Co may be used to fabricate SV sensorsaccording to the present invention.

While the present invention has been particularly shown and describedwith reference to the preferred embodiments, it will be understood bythose skilled in the art that various changes in form and detail may bemade without departing from the spirit, scope and teaching of theinvention. Accordingly, the disclosed invention is to be consideredmerely as illustrative and limited in scope only as specified in theappended claims.

We claim:
 1. A spin-valve (SV) magnetoresistive sensor, comprising:a seed layer of non-magnetic alloy of Ni--Fe--Cr deposited on a substrate; a free layer of ferromagnetic material deposited over said seed layer; a spacer layer of non-magnetic material deposited over said free layer; a pinned layer of ferromagnetic material deposited over said spacer layer; and antiferromagnetic (AFM) layer deposited over said pinned layer for pinning the magnetization of said pinned layer.
 2. The SV sensor as recited in claim 1, wherein said free layer includes first and second free sub-layers where said first free sub-layer is made of a ferromagnetic material which is different from said second free sub-layer ferromagnetic material.
 3. The SV sensor as recited in claim 2, wherein said first free sub-layer is made of cobalt and said second sub-layer is made of Ni--Fe.
 4. The SV sensor as recited in claim 1, wherein said spacer layer is selected from a group of material consisting of copper, gold and silver.
 5. The SV sensor as recited in claim 1, wherein said AFM layer is made of Ni--Mn.
 6. The SV sensor as recited in claim 1, wherein said AFM layer is selected from a group of material consisting of Fe--Mn, Pd--Mn, Pt--Mn, Pd--Pt--Mn, Ir--Mn, Rh--Mn, Cr--Mn--Pt and Ru--Mn.
 7. A spin-valve (SV) magnetoresistive sensor, comprising:a seed layer of non-magnetic alloy of Ni--Cr deposited on a substrate; a free layer of ferromagnetic material deposited over said seed layer; a spacer layer of non-magnetic material deposited over said free layer; a pinned layer of ferromagnetic material deposited over said spacer layer; and antiferromagnetic (AFM) layer deposited over said pinned layer for pinning the magnetization of said pinned layer.
 8. The SV sensor as recited in claim 7, wherein said free layer includes first and second free sub-layers where said first free sub-layer is made of a ferromagneic material which is different from said second free sub-layer ferromagnetic material.
 9. The SV sensor as recited in claim 8, wherein said first free sub-layer is made of cobalt and said second sub-layer is made of Ni--Fe.
 10. The SV sensor as recited in claim 7, wherein said spacer layer is selected from a group of material consisting of copper, gold and silver.
 11. The SV sensor as recited in claim 7, wherein said AFM layer is made of Ni--Mn.
 12. The SV sensor as recited in claim 7, wherein said AFM layer is selected from a group of material consisting of Fe--Mn, Pd--Mn, Pt--Mn, Pd--Pt--Mn, Ir--Mn, Rh--Mn, Cr-MN-Pt and Ru--Mn.
 13. A disk drive system, comprising:a magnetic recording disk; a spin valve (SV) magnetoresistive sensor for sensing magnetically recorded data on said disk, the SV sensor comprising:a seed layer of non-magnetic alloy of Ni--Fe--Cr deposited on a substrate; a free layer of ferromagnetic material deposited over said seed layer; a spacer layer of non-magnetic material deposited over said free layer; a pinned layer of ferromagnetic material deposited over said spacer layer; and an antiferromagnetic (AFM) layer deposited over said pinned layer for pinning the magnetization of said pinned layer; an actuator for moving said SV sensor across the magnetic recording disk so the SV sensor may access different regions of magnetically recorded data on the magnetic recording disk; and a recording channel coupled electrically to the SV sensor for detecting changes in resistance of the SV sensor caused by rotation of the magnetization axis of the free ferromagnetic layer relative to the fixed magnetization of the pinned layer in response to magnetic fields from the magnetically recorded data.
 14. The disk drive system as recited in claim 13, wherein said free layer includes a first and a second free sub-layer where said first free sub-layer is made of a ferromagneic material which is different than said second free sub-layer ferromagnetic material.
 15. The disk drive system as recited in claim 14, wherein said first free sub-layer is made of cobalt and said second sub-layer is made of Ni--Fe.
 16. The disk drive system as recited in claim 13, wherein said spacer layer is selected from a group of material consisting of copper, gold and silver.
 17. The disk drive system as recited in claim 13, wherein said AFM layer is made of Ni--Mn.
 18. The disk drive system as recited in claim 13, wherein said AFM layer is selected from a group of material consisting of Fe--Mn, Pd--Mn, Pt--Mn, Pd--Pt--Mn, Ir--Mn, Rh--Mn, Cr--Mn--Pt and Ru--Mn.
 19. A disk drive system, comprising:a magnetic recording disk; a spin valve (SV) magnetoresistive sensor for sensing magnetically recorded data on said disk, the SV sensor comprising:a seed layer of non-magnetic alloy of Ni--Cr deposited on a substrate; a free layer of ferromagnetic material deposited over said seed layer; a spacer layer of non-magnetic material deposited over said free layer; a pinned layer of ferromagnetic material deposited over said spacer layer; and an antiferromagnetic (AFM) layer deposited over said pinned layer for pinning the magnetization of said pinned layer; an actuator for moving said SV sensor across the magnetic recording disk so the SV sensor may access different regions of magnetically recorded data on the magnetic recording disk; and a recording channel coupled electrically to the SV sensor for detecting changes in resistance of the SV sensor caused by rotation of the magnetization axis of the free ferromagnetic layer relative to the fixed magnetization of the pinned layer in response to magnetic fields from the magnetically recorded data.
 20. The disk drive system as recited in claim 19, wherein said free layer includes a first and a second free sub-layer where said first free sub-layer is made of a ferromagnetic material which is different than said second free sub-layer ferromagnetic material.
 21. The disk drive system as recited in claim 20, wherein said first free sub-layer is made of cobalt and said second sub-layer is made of Ni--Fe.
 22. The disk drive system as recited in claim 19, wherein said spacer layer is selected from a group of material consisting of copper, gold and silver.
 23. The disk drive system as recited in claim 19, wherein said AFM layer is made of Ni--Mn.
 24. The disk drive system as recited in claim 19, wherein said AFM layer is selected from a group of material consisting of Fe--Mn, Pd--Mn, Pt--Mn, Pd--Pt--Mn, Ir--Mn, Rh--Mn and Ru--Mn.
 25. A spin valve (SV) magnetoresistive sensor, comprising:a seed layer deposited on a substrate, wherein said seed layer is made of a non-magnetic alloy of (Ni_(a) --Fe_(b))_(x) --Cr_(y) where 45% >a>100%, 0%>b>55%, 50%>x>80%, 20%>y>50%, a+b=100%, and x+y=100%; a free layer of ferromagnetic material deposited over said seed layer; a spacer layer of non-magnetic material deposited over said free layer; a pinned layer of ferromagnetic material deposited over said spacer layer; and an antiferromagnetic (AFM) layer deposited over said pinned layer for pinning the magnetization of said pinned layer.
 26. A spin valve (SV) magnetoresistive sensor, comprising:a seed layer deposited on a substrate, wherein said seed layer is made of a non-magnetic alloy of Ni_(x) --Cr_(y) where 50%>x>80%, 20%>y>50%, and x+y=100%; a free layer of ferromagnetic material deposited over said seed layer; a spacer layer of non-magnetic material deposited over said free layer; a pinned layer of ferromagnetic material deposited over said spacer layer; and an antiferromagnetic (AFM) layer deposited over said pinned layer for pinning the magnetization of said pinned layer. 